1. Field of the Invention
The present invention relates to an estimation method for a film having the optical anisotropy due to the alignment of molecules, for example, a liquid crystal alignment layer and the like which provides the initial orientation to the liquid crystal molecules in a liquid crystal display device.
2. Description of the Related Art
The crystal rotation method (described by T. J. Scheffer and J. Nehring in Journal of Applied Physics, Vol. 48, pp.1783, 1977) has been widely employed as an optical method of measuring an angle that liquid crystal molecules in an antiparallel cell make with the reverse of a substrate. In this method, with the linearly polarized light incident on the sample, the optical retardation(phase shift) of the transmitted light which is generated through birefringence is measured as a function of the incident angle. On the other hand, instead of the direct measurement of the dependence of the polarization in the transmitted light on the incident direction, another measuring method in which an analyzer is placed behind a sample and the quantity of light transmitted through the analyzer is monitored as a function of the incident angle is also widely utilized.
However, the above-mentioned conventional techniques have the following problems as pointed out, for example, by K.-Y. Han et al. in Japanese Journal of Applied Physics, Vol. 32, pp. L1242-1244,L277-279 1993.
That is, because the liquid crystal is held between a pair of glass substrates, the refraction at the substrate causes a shift in the incident position of the light on the liquid crystal section, as the incident angle is changed. As the place through which the light passes within the liquid crystal is varied, the polarization of the transmitted light directly reflects the variance in thickness of the liquid crystal layer with the place, which hinders the accurate measurements. The incident angle of the light on the sample is usually changed by rotating the sample, and thus the relative position between the incident light and the transmitted light also changes, accompanying with the sample rotation. As a result, in order to carry out an accurate polarization measurement of the transmitted light, it is necessary for the positions of an analyzer and the like to be adjusted according to the thickness, the material and the rotation angle of the sample and the measuring efficiency of this method becomes low.